Stoichiometry & the Mole

The Mole __________ - SI base unit used to measure the amount of a substance. A mole of anything contains __________ representative particles.

Mole – Representative Particle Calculations Calculate the number of atoms in 3.50 moles of copper

Mole – Mass Relationship __________ - mass in grams of one mole of any pure substance

Calculating Molecular Mass What is the molecular mass of (C 3 H 5 ) 2 S?

Mole – Mass Calculations How many moles of Ca(OH) 2 are in 325 grams?

Mass – Particle Conversions How many atoms of gold are in 25.0 g of gold?

Mass – Mass Relationships Ammonium nitrate decomposes into dinitrogen monoxide gas and water. Determine that amount of water produced if 25.0 g of ammonium nitrate decomposes.

Limiting Reactants A chemical reaction will stop when you run out of one of your products __________– limits the extent of the reaction.  Determines the amount of product that is formed.  It runs out first __________– left over reactant

Example S 8 + 4Cl 2  4S 2 Cl g of S 8 and g of Cl 2 are combined in a flask. How much S 2 Cl 2 will you get?

Other questions What was the limiting reactant? What was the excess reactant? How much excess did we have left over after the reaction was completed?

% Yield % = (part / whole) x 100

% Yield ____________________– the amount of product you should get if the experiment went perfectly.  You get this number from stoichiometry ____________________– this is what you actually got in the lab.  You measure this on a balance ____________________– how close you were to the correct answer  % yield = (actual / theoretical) x 100

% Yield Example K 2 CrO 4 + 2AgNO 3  Ag 2 CrO 4 + 2KNO 3 What is the theoretical yield of Ag 2 CrO 4 formed from g AgNO 3 ? What is the % yield if g is actually formed?

% Composition % = (part / whole ) x 100 Calculate the % Composition of iron (III) oxide

Empirical & Molecular Formulas ____________ – the smallest whole number ratio of elements ____________– the true number of elements in a compound

Steps for Calculating the Empirical Formula 1. List your givens 2. Change % to grams 3. Change grams to moles 4. Divide everything by the smallest number of moles 5. Write your formula

Empirical Formula Problem Calculate the empirical formula for a compound containing g C, 8.16 g H, and g O.

Steps for Calculating Molecular Formula 1. Calculate the empirical formula 2. Get the molecular mass of the empirical formula that you just determined 3. Divide the experimentally determined molecular mass (given) by the molecular mass of the empirical formula 4. You will get a whole number 5. Multiply everything in the empirical formula by this number

Molecular Formula Problem Calculate the molecular formula of a compound containing 40.68%C, 5.08%H, and 54.25%O with an experimentally determined molecular weight of g/mol

Empirical Formula with Combustion Data Steps 1. Convert g CO 2 to g C 2. Convert g H 2 O to g H 3. Subtract to get g of other element 4. Work Empirical Formula problem as usual

Example A compound is comprised of carbon, hydrogen, and nitrogen. When g of this compound is reacted with oxygen, g of CO 2 and g of water are collected. Assuming that all of the carbon in the compound is converted into CO 2, determine the empirical formula of the compound.

Example

One more example A g hydrocarbon sample was combusted to yield g CO 2 and g H 2 O. The molecular mass was determined to be 116 g/mol. Determine the empirical and molecular formulas of the compound.